Two
astronauts floated outside the International Space Station late Monday to
install new experiments that will study the harsh orbital environment and help explain
recent glitches with Russian Soyuz spacecraft.

Clad in
Russian-built spacesuits, station
commander Michael Fincke of NASA and flight engineer Yury Lonchakov spent
more than five hours working outside the orbiting laboratory to attach the new
science equipment. The only hitch popped up late in the spacewalk, when a
problematic data relay for a joint Russian-European experiment thwarted
repeated attempts to install it.

?Okay,
going out into space again,? said Fincke, who made his fifth career spacewalk
in the excursion. ?Excellent! It?s good to be here again.?

Lonchakov,
a cosmonaut with Russia?s Federal Space Agency, led the five-hour, 38-minute
spacewalk with Fincke while their NASA crewmate Sandra Magnus monitored their
progress from inside the space station. The spacewalk began at 7:51 p.m. EST
(0051 Dec. 23 GMT), about 40 minutes late, due to a pressure valve glitch.

The
spacewalkers swiftly accomplished their primary task to install a so-called
Langmuir probe near their airlock hatch of the space station?s Russian-built
Pirs docking compartment. The tool is designed to measure the surrounding plasma and electromagnetic
environment.

Data from
the probe is expected to help Russian engineers pin down the cause of explosive
bolt malfunctions that sent two of the last three Soyuz spacecraft that
ferried station astronauts back to Earth to suffer module separation glitches
during their descents. The malfunctions, in October
2007 and April 2008, forced the Soyuz vehicles into off-target landings and
subjected their crews to higher gravitational stresses than nominal landings.

Russian
engineers believe that electrical arcs or other electromagnetic interference
near the space station?s Soyuz docking ports may have prompted the explosive
bolt failures. A suspect bolt was removed from the last Soyuz to land prior to
its Oct. 24 descent this year and it touched down on target as planned.

But Russian
engineers hope the new plasma probe outside the station will yield more
insights.

?It?s
definitely a step in that process,? said Kirk Shireman, NASA?s deputy space
station program manager. ?There?s still a ways to go in the overall
understanding and confirmation of the root cause that we have on the Soyuz.?

In addition
to attaching the plasma probe, Lonchakov and Fincke retrieved a Russian
experiment canister of biological samples from the space station?s hull. They
also installed a Russian plasma physics experiment called Impuls to the
exterior of the station?s
Zvezda service module, at times working uncomfortably closed to a solar
array, which they asked flight controllers to move to give them more room.

?I?m very
close to the solar array,? Fincke said. ?It?s very important that nothing be
broken here.?

But it was
a second experiment, dubbed EXPOSE-R, which refused to activate properly after
the spacewalkers installed it near Impuls. A joint project between the European
and Russian space agencies, the experiment is designed to understand how
organic materials are affected when exposed directly to space.

Despite repeated
efforts to activate it, flight controllers at Russia?s Mission Control near
Moscow were unable to receive any telemetry from the device via a data relay
connector. Flight controllers eventually ordered Fincke and Lonchakov to remove
the experiment and return it back inside the International Space Station.

?We had to
remove the entire EXPOSE-R because of one connector,? said a disappointed
Lonchakov. ?Yes, that?s a shame.?

Monday
night?s spacewalk marked the 19th excursion outside the space station this year
and the 119th dedicated to construction and maintenance of the orbiting
laboratory since its first element launched in 1998. Fincke ended his fifth
spacewalk with 21 hours and 23 minutes of spacewalking time. Lonchakov,
meanwhile, ended with five hours and 38 minutes in his spacewalking debut.

?Yury, was
it beautiful?? Magnus asked after the spacewalk.

?Yes it was
beautiful, although we really had no time to look around,? Lonchakov replied.